Perfusion assessment using transmission laser speckle imaging

Abstract

Methods and apparatus for measuring perfusion using transmission laser speckle imaging are provided. The apparatus comprises a coherent light source and a detector configured to measure transmitted light associated with an unfocused image at one or more locations. The coherent light source and detector are positioned in a transmission geometry. The apparatus further comprises means for securing the coherent light source and the detector to the tissue sample in a fixed transmission geometry relative to the tissue sample. The apparatus may further comprise at least one processor to receive information from the detector and process detected variations in transmitted light intensity to determine a single metric of perfusion. The method may comprise the steps transilluminating a tissue sample with coherent light, recording spatial and/or temporal variations in the transmitted light signal, determining speckle contrast value(s), and computing a metric of perfusion.

What is claimed is: 
     
       1. An apparatus comprising:
 a coherent light source configured to illuminate a tissue sample; 
 a digital camera sensor comprising a plurality of light-sensitive elements configured to capture a plurality of light intensity values; 
 an enclosure configured to accommodate the tissue sample, the enclosure being coupled to the coherent light source and the digital camera sensor, wherein the enclosure is configured to position the coherent light source no more than 5 mm from the tissue sample and to position the digital camera sensor no more than 10 mm from the tissue sample, wherein the enclosure is configured to position the coherent light source and the digital camera sensor on opposing sides of the tissue sample; and 
 a processor, 
 wherein the enclosure is configured to be affixed to the tissue sample such that the enclosure cannot move independently from the tissue sample, 
 wherein the digital camera sensor is configured to transfer the plurality of light intensity values to the processor, and 
 wherein the processor is configured to:
 determine an average of at least some light intensity values of the plurality of light intensity values; and 
 compute, based on at least the average, a speckle contrast parameter indicative of tissue perfusion in the tissue sample. 
 
 
     
     
       2. The apparatus of  claim 1 , wherein the enclosure is configured to position the light source and the digital camera sensor in a transmission geometry with respect to the tissue sample. 
     
     
       3. The apparatus of  claim 1 , wherein the enclosure is configured to position at least one of: the light source in direct contact with the tissue sample, or the digital camera sensor in direct contact with the tissue sample. 
     
     
       4. The apparatus of  claim 1 , wherein the tissue sample is a soft tissue perfused with blood vessels. 
     
     
       5. The apparatus of  claim 4 , wherein the tissue sample is a digit, an earlobe, or a nostril. 
     
     
       6. The apparatus of  claim 1 , wherein the digital camera sensor comprises image-forming optics which have a front focal distance and wherein the enclosure is configured to position the image-forming optics a distance from the tissue sample not equal to the front focal distance. 
     
     
       7. The apparatus of  claim 1 , wherein the enclosure is configured to position the digital camera sensor a fixed distance from the tissue sample and the apparatus is configured so that the digital camera sensor captures light from a fixed field of view. 
     
     
       8. The apparatus of  claim 7 , wherein the fixed field of view is configured to capture light from only a portion of the tissue sample. 
     
     
       9. The apparatus of  claim 8 , wherein the fixed field of view is sized to enable the processor to determine the speckle contrast parameter without mapping areas of relatively high blood flow and areas of relatively low blood flow in the tissue sample within a single image. 
     
     
       10. The apparatus of  claim 8 , wherein the apparatus is configured to achieve a pixel to speckle size ratio of at least 2:1. 
     
     
       11. The apparatus of  claim 1 , wherein the digital camera sensor comprises more than two pixels. 
     
     
       12. The apparatus of  claim 1 , wherein the speckle contrast parameter is defined as a standard deviation of the at least some of the light intensity values divided by the average of the at least some of the light intensity values. 
     
     
       13. The apparatus of  claim 1 , wherein the enclosure comprises a space for receiving the tissue sample, the space being no larger than a space configured to receive a human digit. 
     
     
       14. The apparatus of  claim 1 , further comprising an opaque sheet having an aperture positioned in front of the digital camera sensor such that the aperture is configured to be positioned between the digital camera sensor and the tissue sample. 
     
     
       15. The apparatus of  claim 14 , wherein the opaque sheet is configured to be placed against the tissue sample by the enclosure without any separation distance between the tissue sample and the opaque sheet. 
     
     
       16. The apparatus of  claim 14 , wherein the opaque sheet is configured to be placed less than 10 mm from the digital camera sensor. 
     
     
       17. The apparatus of  claim 14 , wherein the aperture is 1 mm in diameter. 
     
     
       18. The apparatus of  claim 1 , wherein the apparatus is sufficiently compact enough to be freely supported by a single human finger. 
     
     
       19. The apparatus of  claim 1 , wherein the processor is configured to determine, based on the speckle contrast parameter, a metric of the tissue perfusion in the tissue sample. 
     
     
       20. A method of determining a speckle contrast parameter indicative of perfusion in a soft tissue sample, the method comprising:
 placing a soft tissue sample perfused with blood vessels within an enclosure of an apparatus, the apparatus comprising:
 a coherent light source configured to illuminate the soft tissue sample; and 
 a digital camera sensor comprising a plurality of light-sensitive elements configured to capture a plurality of light intensity values from the soft tissue sample and configured to transfer the plurality of light intensity values to a processor, 
 wherein the enclosure is coupled to the coherent light source and the digital camera sensor and fixes the coherent light source and the digital camera sensor in a fixed spatial relationship with respect to the soft tissue sample such that neither can move independently of the soft tissue sample or independently of the other during use, wherein the enclosure is configured to position the coherent light source no more than 5 mm from the soft tissue sample and to position the digital camera sensor no more than 10 mm from the soft tissue sample, wherein the enclosure is configured to position the coherent light source and the digital camera sensor on opposing sides of the soft tissue sample, and 
 wherein the apparatus is configured such that the digital camera sensor captures a fixed field of view of a portion of the soft tissue sample; 
 
 illuminating the soft tissue sample with the coherent light source; 
 capturing with the digital camera sensor an image from the fixed field of view comprising the plurality of light intensity values; 
 determining, with the processor, an average of at least some light intensity values of the plurality of light intensity values; and 
 computing, with the processor, the speckle contrast parameter indicative of tissue perfusion in the tissue sample based on at least the average. 
 
     
     
       21. The method of  claim 20 , wherein the captured image is an unfocused image. 
     
     
       22. The method of  claim 20 , wherein computing the speckle contrast parameter comprises computing the speckle contrast parameter without mapping blood flow within the soft tissue sample. 
     
     
       23. The method of  claim 20 , further comprising calculating, with the processor, a metric of perfusion directly from the speckle contrast parameter.